Children's Cancer Study Group is engaged in the conduct of clinical trials in pediatric cancer which are designed to improve the survival and quality of survival in children with cancer as well as to obtain information which addresses more basic questions in tumour biology. Denver Children's Hospital became a full member of CCSG in January, 1980, having participated in CCSG and Intergroup protocol studies since July, 1979. This proposal requests support to continue our contribution to CCSG efforts. Denver Children's Hospital is providing scientific leadership to CCSG in the areas of brain tumors and leukemia. The multidisciplinary team at Children's Hospital is the referral center for the evaluation and treatment of children with cancer from the entire eastern Rocky Mountain Region, assuring a large number of children for entry into protocol studies. Past and present research at Children's Hospital is and will continue to provide impetus for group wide activities.